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Full-Text Articles in Engineering

Minimizing The Radiated Sound Power With Minimal Structural Modification , Daniel Henry Kruger Jan 1995

Minimizing The Radiated Sound Power With Minimal Structural Modification , Daniel Henry Kruger

Retrospective Theses and Dissertations

In cases where a structure's excitation cannot be altered, the sound radiation from the structure must be minimized by modifying the structure within given design constraints. This dissertation considers minimizing sound radiated by an existing structure with minimal changes to the structure itself. To accomplish this the sound power radiated by a structure was written as a function of the normal surface velocity using the boundary element method. The feasibility of reducing radiated sound power with small patches of constrained layer damping material is proved. Small patches of constrained layer damping material are placed on the structure to effectively ...


Development Of An Acoustic Microscope To Measure Residual Stress Via Ultrasonic Rayleigh Wave Velocity Measurements , Jane Carol Johnson Jan 1995

Development Of An Acoustic Microscope To Measure Residual Stress Via Ultrasonic Rayleigh Wave Velocity Measurements , Jane Carol Johnson

Retrospective Theses and Dissertations

High stress in a crucial instrument part can cause failure. Stress detection is one of the aims of nondestructive testing. The velocity change of acoustic waves can be used to detect stress in a material. An acoustic microscope is an instrument which induces and detects acoustic waves and in one mode of operation, is able to measure the velocity of acoustic surface waves. It does this over a very small area and is capable of high spatial resolution;One of the challenges in the measurement of stress is the achievement of high spatial resolution. Since the stress induced velocity shifts ...


Parallel Surface Reconstruction Through Virtual Milling , Kumaran Kalyanasundaram Jan 1995

Parallel Surface Reconstruction Through Virtual Milling , Kumaran Kalyanasundaram

Retrospective Theses and Dissertations

Surface definition deals with representing a surface analytically using a finite number of parameters and with acceptable levels of error. In the past few years it has become a key discipline in Computational Fluid Dynamics (CFD). Recent advances in computers and numerical algorithms have made it possible for CFD practitioners to attempt flow solutions about complex three-dimensional geometries. The first step in this process is having a numerical representation of the shape. In many cases of interest such a representation already exists; i.e., aircraft designed on a computer. Such Computer-Aided Design (CAD) descriptions do not exist, though, for objects ...


Numerical Investigation Of Type Ii Non-Newtonian De/Anti-Icing Fluid Effects On Take-Off Performance For General Aviation Aircraft , Dennis James Cronin Jan 1995

Numerical Investigation Of Type Ii Non-Newtonian De/Anti-Icing Fluid Effects On Take-Off Performance For General Aviation Aircraft , Dennis James Cronin

Retrospective Theses and Dissertations

Ground icing, while preventable with glycol based freezing point depressant fluids, accounts for nearly 40-50 civil accidents a year according to one account. More viscous than Type I fluids, Type II fluids are inherently non-linear in their shear stress-rate of strain relationship having smaller relative viscosity at higher shear rates. The non-linearity makes properly scaled wind-tunnel testing difficult and computational methods are employed in this study to look at the aerodynamic effects of the deicing fluid on global performance during typical take-off maneuvers for general aviation. The method is tested on a two-dimensional NACA 0012 airfoil under typical take-off simulation ...


Adaptive Nonlinear Attitude Control Of Spacecraft , Cheng Tang Jan 1995

Adaptive Nonlinear Attitude Control Of Spacecraft , Cheng Tang

Retrospective Theses and Dissertations

Three adaptive nonlinear control approaches are proposed for attitude control of a Space Station. These control algorithms avoid the need for linearization, either by truncating a Taylor series or by a feedback linearization approach, which poses some difficulties in the presence of both uncertain mass properties and external disturbances. Global stability of the Space Station is guaranteed;A conventional linear-quadratic regulator synthesis technique is investigated. This linear control scheme provides a natural way to select control gains for the known spacecraft system parameters. Simulation results reveal that the uncertain mass property causes the nonlinear Space Station to be uncontrollable;On ...


Optimal Turning Maneuvers For Six-Degree-Of-Freedom High Angle-Of-Attack Aircraft Models , Jen-Nai Chou Jan 1995

Optimal Turning Maneuvers For Six-Degree-Of-Freedom High Angle-Of-Attack Aircraft Models , Jen-Nai Chou

Retrospective Theses and Dissertations

Various Minimum-Time Turning Maneuvers for two high angle-of-attack, six-degree-of-freedom, aircraft models have been investigated. The primary aircraft model is for a nonlinear 6-DOF F-16 fighter aircraft with high angle-of-attack maneuverability. The other model is for a linearized 6-DOF F-18 fighter which also can be flown in the high angle-of-attack range. Standard 6-DOF equations are employed except that the Quaternion attitude representation system is used instead of Euler Angles to avoid the pitch angle singularity of Euler Angles;These Optimal Control problems have been transformed into Nonlinear Programming problems via Parameter Optimization techniques. Different parameterization techniques were tested on the Van ...


Coupled Compressible And Incompressible Finite Volume Formulations For The Large Eddy Simulation Of Turbulent Flow With And Without Heat Transfer , Wen-Ping Wang Jan 1995

Coupled Compressible And Incompressible Finite Volume Formulations For The Large Eddy Simulation Of Turbulent Flow With And Without Heat Transfer , Wen-Ping Wang

Retrospective Theses and Dissertations

A coupled finite volume approach for solving the time-dependent Navier-Stokes equations is developed for application to the large eddy simulation (LES) of turbulent flow. The preconditioning strategy of coupling the incompressible N-S equations and providing acceleration of iterative convergence in both compressible and incompressible formulations is employed. Three different spatial discretization schemes along with the regular/staggered grid arrangements are evaluated on both two-dimensional laminar flows and three-dimensional turbulent flows;No distinctive differences are found in laminar flow cases, but the staggered grid appears to provide a better resolution of the turbulence statistics over a regular one in the simulation ...


Computer Simulation Of Coronary Blood Flow , Brian Christopher Frake Jan 1995

Computer Simulation Of Coronary Blood Flow , Brian Christopher Frake

Retrospective Theses and Dissertations

A computer model to simulate coronary fluid dynamics has been developed which can give some insight into the role of hemodynamics in health and disease. Although this study focuses mainly on coronary blood flow, the complete model consists of all major branches of the systemic circulation as well as the left epicardial coronary circulation;The flow equations are obtained by integrating the one-dimensional continuity and momentum equations over the cross-section of the artery to give a relationship between the primary variables of interest, the pressure and flowrate. An arctangent model was used as a constitutive equation to describe the pressure-area ...


Ultrasonic Nondestructive Evaluation Techniques And The Effects Of Fiber Architecture On Mechanical Performance In Multi-Directionally Reinforced Textile Composites , Richard Douglas Hale Jan 1995

Ultrasonic Nondestructive Evaluation Techniques And The Effects Of Fiber Architecture On Mechanical Performance In Multi-Directionally Reinforced Textile Composites , Richard Douglas Hale

Retrospective Theses and Dissertations

Constant load stress rupture tests were performed on alloy 908. The test matrix used varied oxygen concentration, applied load, temperature, and percent cold work. The effect of modifying surface residual stresses on intergranular oxidation and cracking was examined using constant strain C-ring tests;The mechanism for high temperature intergranular fracture in alloy 908 is stress assisted intergranular oxidation cracking. A direct correlation between percent intergranular fracture and oxygen concentration was observed. This result was comparable to the oxidation assisted, intergranular fracture behavior of alloy 718. Internal oxidation, for temperatures at or near 650∘ C and under an applied tensile stress ...


Ultrasonic Scattering From Decorated Grain Boundaries , John Mittleman Jan 1995

Ultrasonic Scattering From Decorated Grain Boundaries , John Mittleman

Retrospective Theses and Dissertations

The microstructure of polycrystalline materials is manipulated in many ways to create materials with superior engineering properties. Alloying pure materials, for example, can alter crystallographic structure to strengthen or stiffen the material, but when impurities collect along grain boundaries, the material may become embrittled. This undesirable condition is generally associated with improper heat treatment during fabrication, but it may also occur during the service life of alloys exposed to penetrating radiation or severe thermal conditions. This dissertation studies scattering from decorated grain boundaries theoretically and experimentally, and ties results for isolated scatterers to grain noise measurements on materials composed entirely ...